Morphology, ecology and biogeography of Stauroneis pachycephala P.T. Cleve (Bacillariophyta) and its transfer to the genus Envekadea

Abstract

Stauroneis pachycephala was described in 1881 from the Baakens River, Port Elizabeth, South Africa. Recently, it was found during surveys of the MacKenzie River (Victoria, Australia), the Florida Everglades (USA) and coastal marshes of Louisiana (USA). The morphology, ecology and geographic distribution of this species are described in this article. This naviculoid species is characterised by lanceolate valves with a gibbous centre, a sigmoid raphe, an axial area narrowing toward the valve ends, and capitate valve apices. The central area is a distinct stauros that is slightly widened near the valve margin. The raphe is straight and filiform, and the terminal raphe fissures are strongly deflected in opposite directions. Striae are fine and radiate in the middle of the valve, becoming parallel and eventually convergent toward the valve ends. The external surface of the valves and copulae is smooth and lacks ornamentation. We also examined the type material of S. pachycephala. Our observations show this species has morphological characteristics that fit within the genus Envekadea. Therefore, the transfer of S. pachycephala to Envekadea is proposed and a lectotype is designated.

Keywords:

• diatoms
• morphology
• Stauroneis pachycephala
• ecology
• Envekadea
• biogeography
• taxonomy
• lectotype

Acknowledgements

This research was supported by the Iowa Lakeside Laboratory scholarship and Federation University Australia scholarship to IA. This project was funded by Grampians Wimmera Mallee Water (GWMWater, Australia). IA wishes to thank Peter J. van der Linden (Executive Director of Iowa Lakeside Laboratory & Regent's Resource Center, USA) and all staff and students at the Iowa Lakeside Laboratory for their help and cooperation. The authors would like to thank Rosie Grundell, Wendy Cloke, Jessica Reeves and Phuong Doan (Federation University Australia), and Rebecca Bixby (University of New Mexico) for their help and cooperation. The authors also would like to give special thanks to Evelyn Gaiser (Florida International University) for providing data on E. pachycephala in the Florida Everglades. We thank two anonymous reviewers, Eileen J. Cox (Natural History Museum, UK) and Lisa Osterman (U.S. Geological Survey) for their valuable comments that greatly improved the manuscript.